Perfect binding is very popular because it is much faster and less expensive than side sewing or spine sewing, and it can be used to manufacture books which are too thick for saddle stitching. However, conventional perfect binding has the disadvantage that the pages are not held at the spine with the strength of sewn books. This, therefore, limits the categories of books to which perfect binding may be applied.
Children's books are a very specialized category because they must be capable of standing up to rough handling; so publishers of such books have generally considered it necessary to have them sewn for strength. This, however, adds greatly to the cost of such books and correspondingly limits the market for them.
Accordingly, a need has existed for many years for a method of binding books which is capable of producing books comparable in binding strength to books with sewn bindings but at about the cost of perfect binding. The need has, of course, become more acute as the cost of book manufacture increases; and for several years the cost of sewn, case-bound books has indicated such a need in a broad range of books.